it was designed by a company called sdori they are based out of san diego, ca... they specialize in making hte spacers for both 4x4 and now 4x2 toyotas as i helped them design the 4x2 ones... they allow an extra 1.5" between the balljoint and the upper control arm... geometry slightly changes and i know have to correct camber issues, but i gained a little bit over an inch in ride height... also, with the ifs, i know can droop the tire another 1.5" lower than stock... anotehr advantage is that it allows the tire when compressed to have another 1.5" of clearance before hitting the body.....
check out
www.sdori.com for info on what the spacers are/do